Culmen

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The culmen or culmen ridge is a part of a bird's bill. It is the external ridge along the outer part of the centre of the upper mandible, formed where the two halves of the mandible join.

The shape of the culmen can be a useful identification feature. For example, the shape of the culmen differs markedly between the Common Guillemot (evenly, shallowly curved) and the Brünnich's Guillemot, which has a more abrupt angle to its culmen. The same can apply to the colour or patterning — White-billed Diver has a completely pale culmen, whereas on the similar Great Northern Diver this area is dark.

The length of the culmen is often measured during bird ringing.

[edit] See also

• Gonys